In a recent electronically-controlled vehicle, its reliability and stability are ensured by technology disclosed by Patent Literature 1 (JP H6-50851 A), for example. The disclosed apparatus is provided with an in-vehicle data storage unit and a diagnostic unit. The in-vehicle data storage unit reads and stores input-output data of an in-vehicle electronic control unit. The diagnostic unit reads the data stored in the in-vehicle data storage unit, and compares the data with specified criterion value to determine whether a failure exists.
A vehicle control system is provided with multiple computing units, such as a computing unit (electronic control unit) which controls an engine, a computing unit which controls a transmission, and a computing unit which controls an Air-Con (air-conditioner). In a case that each computing unit has an abnormality-diagnosis circuit, it is likely that a requirement of cost reduction may not be satisfied, which is an important technological issue.
The present applicant has been researching a vehicle control system in which an output signal of a first computing unit is input into a second computing unit to determine whether the output signal of the first computing unit is normal by the second computing unit (input computing unit), whereby an abnormality diagnosis of the first computing unit (output computing unit) is performed. In the above research process, following new subjects has become clear.
Due to some causes (for example, data corruption of ROM etc.), it is likely that a criterion value for the abnormality diagnosis of the first computing unit may become an abnormal value. When the abnormality diagnosis of the first computing unit is performed based on the abnormal criterion value, it is more likely that the abnormality diagnosis of the first computing unit may be erroneously performed. Since the abnormality of the criterion value is undetectable without a monitoring function for monitoring the criterion value, an erroneous abnormality diagnosis cannot be avoided, so that an accuracy of the abnormality diagnosis may deteriorate. Also, the above Patent Literature 1 does not disclose a technology to monitor the criterion value.